Applications of the touch input device is quite extensive. Currently, some of the touch input device which is commercially available has two kinds of different input modes simultaneously. Herein, the touch input device has a backlight module, and a first input mode is provided when the backlight module is turned on and thus the touch input device shows a predetermined pattern, while a second input mode is provided when the backlight module is turned off and thus the predetermined pattern is not shown. In another word, users may recognize which input mode it is switched to currently by whether the pattern is shown or not, and then input signals according to the current input mode. For example, when the backlight is turned off, an appearance of the touch input device is presented as a whole black state and the input mode is preset a mode for controlling a mouse cursor. At this time, users can implement motions of moving the mouse cursor and clicking according to the appearance of the touch input device is presented as the whole black state. On the contrary, when the backlight is turned on, a luminous keyboard is presented on the touch input device and the input mode is preset a mode for controlling a keyboard. At this time, users can input letters and symbols by the touch input device according to the appearance is presented as the luminous keyboard pattern. Therefore, one of the design points of such a backlight touch input device is how to ensure that the pattern is not shown when the backlight is turned off, but the luminous pattern is shown only when the backlight is turned on, so as to avoid confusing users.
FIG. 1 illustrates a structural side view of a conventional backlight input device. Referring to FIG. 1, the conventional backlight input device 1 comprises an input interface 11, a backlight module 12 and a Mylar plate 19, wherein a bottom-up sequence thereof is the input interface 11, the backlight module 12 and the Mylar plate 19. Herein, the backlight module 12 comprises a light source 13 and a light guide plate 14, while a lower surface of the Mylar plate 19 is disposed with a plurality of patterns 17. The patterns 17 are printed by using a light transmissive black printing ink with a light shading rate about 98%, and the regions outside the patterns 17 are printed by using an opaque black printing ink to form a light shading layer 18. Thus, the light can pass through the surface of the Mylar plate 19 from where is printed with the patterns 17 only, but is unable to pass through from the regions outside the patterns 17. When the backlight module 12 of the backlight input device 1 is turned off, there is still faint light entering into the backlight input device 1 from the environment. However, the light quantity of the 2% faint light coming from the environment and passing through the regions printed with the patterns 17 is too weak to be distinguished by human eyes due to the light shading rate of the patterns 17 is 98%, and thus the patterns 17 would not be shown on the Mylar plate 19, i.e. users would not see the patterns 17. In contrast, when the backlight module 12 of the backlight input device 1 is turned on, there is a significant amount of light entering into the backlight input device 1. At this time, a difference of the light quantities between the light passing through the regions printed with the patterns 17 and the light coming from the environment is enough to be distinguished by human eyes although there is only 2% light passing through the Mylar plate 19, and thus users can recognize the inputting locations indicated by the luminous patterns 17 on the backlight input device 1.
FIG. 2 illustrates a structural side view of another conventional backlight input device 2. Referring to FIG. 2, the other conventional backlight input device 2 comprises an input interface 21, a backlight module 22 and a surface layer 29, wherein a bottom-up sequence thereof is the input interface 21, the backlight module 22 and the surface layer 29. An upper surface of the surface layer 29 is printed with a shading printing ink, so as to form a light shading layer 28 having a predetermined light shading rate. The backlight module 22 comprises a light source 23 and a light guide plate 24. A lower surface 26 of the light guide plate 24 has at least a pattern 27 formed from micro structures of light guide arranged densely. The destruction of total reflection may happen due to incident angles of the light are capable of being varied by the micro structures of light guide in the light guide plate 24, and thus the light may be refracted to pass through the light guide plate 24. Therefore, when the light quantity in the light guide is sufficient, the light quantity reveals from the top side of the micro structures of light guide is enough to be distinguished by human eyes, and thus the pattern 27 is visible. When the backlight module 22 of the backlight input device 2 is turned off, the light quantity entering into the backlight input device 2 is not sufficient, and thus the pattern 27 would not be shown due to the light quantity passing through the light shading layer 28 is not enough, i.e. users would not see the pattern 27. In contrast, when the backlight module 22 is turned on, the light passing through the light shading layer 28 via the micro structures of light guide is enough to show the luminous pattern 27.
However, both of the two conventional backlight input devices have restrictions in applications. For ensuring that the patterns 17 are not shown when the backlight module 12 is turned off, the conventional backlight input device 1 must use the light transmissive black printing ink with the light shading rate about 98% to print the patterns 17, and thus utilization efficiency of the backlight is only 2%. Therefore, the conventional backlight input device 1 must be equipped with the light source 13 with a high brightness, so as to provide the sufficient light quantity to pass through the light shading layer 28 to show the pattern 27 when the backlight module 22 is turned on, and thus the use cost is increased. In addition, the light shading manners of both of the conventional backlight input device 1 and the conventional backlight input device 2 are disposing a Mylar plate 19 or a surface layer 29 over the light guide plate 24 which is coated with light shading materials on the surface thereof by a screen printing process. However, the screen printing process for coating the light shading materials is complicated, and thus the fabricating cost is further increased as well. Furthermore, the light shading materials coated on the surface of the Mylar plate 19 or the surface layer 29 are likely to fall off due to a long term use or wear and tear during transportation, and thus the life time of the backlight input device may be reduced. Accordingly, it is desired to provide a novel backlight input device to resolve the disadvantages of the conventional backlight input devices.